New York, Rhode Island and Alaska will not report any mail votes on election night. Officials in Michigan and Pennsylvania, two key battleground states, have said full official counts could take several days.

The increase in mail voting could also lead to more provisional votes cast, increasing the number of ballots counted later. In many states, voters who have their eligibility to vote questioned at the polls may cast a provisional ballot, which is set aside and counted only when eligibility is later confirmed.

Usually the number of provisional votes is not large enough to be significant, but there is evidence from early voting that this election may be different. Some voters in at least 22 states are required to vote provisionally if they initially request a mail ballot but decide to vote in person instead (other states have different methods to prevent voting twice). Provisional voting can slow down lines at the polls, and those ballots are generally the last to be reviewed and counted, sometimes weeks after the election.